I think £400 for 2 hours is rather generous, considering the whole point of an RB (from a punter's perspective) is to get the girl cheaper than her rack rate.
You should ask her for 3 hours for £400, TBH, or be bloody cheeky and ask for her to bring a mate for the £400.
But to answer your question, undoubtedly some are thick. I've given up with RBs because despite specific criteria as to age, built, sexual preferences, etc, I got bids from fat birds (clearly outside the size 6 to 12 range) and with no feedback, despite asking for some. Thick doesnt come close if the cannot even comprehend simple requests.